triangle

noun

tri·​an·​gle ˈtrī-ˌaŋ-gəl 

1

: a polygon having three sides compare spherical triangle

2

a

: a percussion instrument consisting of a rod of steel bent into the form of a triangle open at one angle and sounded by striking with a small metal rod

b

: a drafting instrument consisting of a thin flat right-angled triangle of wood or plastic with acute angles of 45 degrees or of 30 degrees and 60 degrees

3

: a situation in which one member of a couple is involved in a love affair with a third person

Illustration of triangle

• 1 equilateral
• 2 acute
• 3 obtuse
• 4 scalene
• 5 isosceles
• 6 right triangle

Examples of triangle in a Sentence

She cut the sandwiches into triangles.

Recent Examples on the Web

Duff, who starred on the network's beloved Lizzie McGuire series, and Lohan, who starred in several Disney original films like Get A Clue and Confessions of a Teenage Drama Queen, sparked rumors of a long-standing feud due to a love triangle involving the late pop star Aaron Carter. —Mekishana Pierre, Entertainment Weekly, 25 Feb. 2026

Anderson had arranged three arrows in the shape of a triangle—each bent over itself, so a viewer seemed to see both sides of a flat strip—all chasing one another in an endless loop. —Beth Gardiner, Time, 24 Feb. 2026

Walk the Blue Fields follows a woman on her wedding day being confronted with a heart-wrenching decision as a love triangle from her past threatens to be revealed. —Justin Kroll, Deadline, 24 Feb. 2026

Striped crane hook and blue triangle, Gateway tunnel project, November 25, 2025. —Nick Paumgarten, New Yorker, 23 Feb. 2026

Word History

Etymology

Middle English, from Anglo-French, from Latin triangulum, from neuter of triangulus triangular, from tri- + angulus angle

First Known Use

14th century, in the meaning defined at sense 1

Phrases Containing triangle

• equilateral triangle
• isosceles triangle
• Pascal's triangle
• right-angled triangle
• right triangle
• spherical triangle
• triangle inequality

Rhymes for triangle

• angle
• bangle
• dangle
• jangle
• mangle
• strangle
• tangle
• wrangle
• disentangle
• entangle
• quadrangle
• untangle

Kids Definition

triangle

noun

tri·​an·​gle ˈtrī-ˌaŋ-gəl 

1

: a figure that has three sides and three angles : a polygon that has three sides

2

: a percussion instrument made of a steel rod bent into a triangle open at one corner which is played by striking with a metal rod

3

: a drafting instrument consisting of a thin flat right-angled triangle

Medical Definition

triangle

noun

tri·​an·​gle ˈtrī-ˌaŋ-gəl 

: a three-sided region or space and especially an anatomical one see anterior triangle, carotid triangle, femoral triangle, posterior triangle, suboccipital triangle